Can't duplicate alpha material setting even though I have all settings in front of me
You beat me to it with answering your own answer (and I'm glad it works for you), but just to clarify i will share what i found:
I believe your tutorial example uses transparency while you use it to a considerable lesser extent (or not at all).
the Transparency color (blue) you used is on the edge of the color circle (while the blue in the example is probably closer to the white center). In this node setup, the more white the color is, the more transparency it causes. Because your blue is relatively dark, the waterfall became less transparent and, in combination with the brown background, visually black.
If you had changed the blue Transparent BSDF color to a color with more white it would be to more like the tutorial example; more transparent.
And I think if you had kept the color the same but changed the Transparent BSDF node to for instance a Diffuse BSDF node you would get a non-transparent waterfall of that color.
But adjusting the ColorRamp also seems to work : )